Gather all ingredients. Preheat the oven to 425 degrees F (220 degrees C).

Mix sweet potatoes, onion, and garlic in a bowl. Drizzle olive oil over the mixture and toss to coat; pour into a shallow roasting pan.

Roast sweet potato mixture in the preheated oven, turning frequently, until the vegetables are soft and golden brown, 30 to 35 minutes.

Remove from the oven. Drizzle balsamic vinegar over the roasted vegetables; season with salt and pepper. Serve hot.